**Rule 1: Universal Rule**

This rule can be used in almost every problems.

If M_{1} persons can do W_{1} work in D_{1} days and M_{2} persons can do W_{2} works in D_{2}days then we can say

M_{1}D_{1}W_{2} = M_{2}D_{2}W_{1}

If the persons work T_{1} and T_{2} hours per day respectively then the equation gets modified to

M_{1}D_{1}T_{1}W_{2} = M_{2}D_{2}T_{2}W_{1}

If the persons has efficiency of E_{1} and E_{2} respectively then,

M_{1}D_{1}T_{1}E_{1}W_{2} = M_{2}D_{2}T_{2}E_{2}W_{1}

**Rule 2:**

If A can do a piece of work in n days, then

The work done by A in one day = 1/n

**Rule 3:**

If A can do a work in D_{1} days and B can do the same work in D_{2} days then A and B together can do the same work

**Rule 4:**

If A is twice as good a workman as B, then A will take half of the time taken by B to complete a piece of work.

**Rule 5:**

If A is thrice as good a workman as B, then A will take one third of the time taken by B to complete a piece of work.

**Rule 6:**

If A and B together can do a piece of work in x days, B and C together can do in y days and C and A together can do in z days, then the same work can be done

**Rule 7:**

If A can do a piece of work in D_{1} days, B can do in D_{2} days and C can do in D_{3}days then they together can do the same work in

**Rule 8:**

If A and B together can do a piece of work in D_{1} days and A alone can do it in D_{2}days, then B alone can do the work in

**Rule 9:**

If the number of men are changed in the ratio of m:n, then the time taken to complete the work will change in the ratio n:m